1. Field of the Invention
The present invention relates in general to the field of ammunition, and it particularly relates to low impulse cartridges. More specifically, the present invention relates to a low impulse telescoping cartridge for use in automatic weapon systems such as the 40 mm MK19 Grenade Machinegun, though the inventive concept is applicable to any caliber of weapon and ammunition.
2. Description of Related Art
An automatic weapon such as the 40 mm MK19 Grenade Machinegun is typically actuated by the direct blowback of the cartridge case against the bolt upon expansion of the propellant gas during the time between cartridge ignition and projectile exit from the barrel. The MK19 Grenade Machinegun is designed to function when firing 40 mm cartridges with a cartridge impulse of approximately 13 to 15 pound-seconds. Reduced cartridge impulses provided by lower mass projectiles and/or reduced chamber pressure will result in reduced energy transferred to the bolt. Consequently, the weapon cyclic rate and reliability will be adversely affected. Exemplary low impulse cartridges that produce much lower impulse levels than required to function the MK19 Grenade Machinegun in the fully automatic mode include blanks, limited range training cartridges, and non-lethal cartridges.
One attempt to achieve reliable weapon function by including a telescoping cartridge case and piston configuration is described in U.S. Pat. No. 5,359,937 to Dittrich. The firearm barrel in Dittrich requires a chamber with an annular step at its forward end or a similar feature for the piston to push against. However, many conventional weapons, including the MK19 Grenade Machinegun do not have such a feature and it would be quite a laborious and expensive undertaking to retrofit the Dittrich design in such conventional weapons.
Therefore, there is a great and still unsatisfied need for a low impulse cartridge which is forced against the rear surface (or breech) of the barrel particularly when the firearm is set in an automatic mode.